The sealing of bearing housings about rotating shafts in a gas turbine engine serves to contain lubricants to cool and lubricate bearing components. Usually axially spaced apart dual seals are used between stationary bearing housings and rotating shafts that have an air plenum between the dual seals. The air plenum is pressurized with compressed air to purge the air plenum of lubricant egress from the bearing housing or ingress of air, liquid contaminants or particles while maintaining engagement between the seal and rotating shaft. At least a minimal clearance gap between stationary and rotating components in the seal area is required to enable assembly, however excessive gaps lead to inefficiencies due to leakage of compressed air from the plenum, leakage of lubricants or ingress of contaminants.
Carbon seals and labyrinth seals are commonly used for this purpose. Carbon seals are less robust and heavier than labyrinth seals in general. Multiple carbon seals are arranged axially along the shaft surface to improve seal performance consuming space axially thus elongating the engine. Carbon seals also add weight and mechanical complexity which are generally undesirable in gas turbine engines, such as aircraft engines.